About Hamburger Safety

Most foodservice professionals know what the RULE is for cooking hamburgers--a core temperature of:

                  150F for 1 minute / 155F for 15 seconds / 160F instant pasteurization                             


It's not the RULE that the industry is too worried about, its how to make it work in a food service establishment or commercial kitchen.  It is an important practical question.  Some say, just cook it so that the inside is not red any more.  It is surprising to find out that many in the industry think that this is a useable indication.  Evidence indicates otherwise.

Color Is Not A Good Clue

  • One out of every four hamburgers turns brown before it's been cooked to a safe internal temperature.

  • And yet, only 3 percent of consumers checked hamburgers with a food thermometer according to a 1998 consumer food safety survey conducted by the Food and Drug Administration and FSIS.

Which of these two burgers was cooked in conformance to the RULE?

Cross-section of a burger cooked to 160 degrees that remained pink inside. Cross-section of a prematurely brown hamburger pattie
This IS a safely cooked hamburger, cooked to an internal temperature of 160 F, even though it's pink inside. This is NOT a safely cooked hamburger. Even though it's brown inside, it is undercooked. Research has shown that some ground beef patties look done at internal temperatures as low as 135 F.

Deeper into the Temperature Issue and the RULE

The science behind the RULE is pretty good, and is based on kill data for the involved pathogen.

Center Temperature (F) Time For a 107 Kill Rate
130

121 minutes

135 38 minutes 
140 12 minutes
145 3.8 minutes 
150 1.2 minutes 
155 23 seconds
160 7.3 seconds 
165

2.3 seconds


It's clear that the kill rate is conservative enough (seven log factor) to ensure that this very bad bug is effectively eliminated from the hamburger. You can also see how the RULE is associated with the bacterial kill data.

The problem is, how do you measure the temperature without dissecting each and every hamburger and probing it with a digital thermometer? 

At Global Sensors, we see the problem in very simple terms:

  1. You need something simple, cheap and effective to stick into the burger to give you an immediate answer (disposable T-Stick), or

  2. You need to cross-calibrate a non-contact thermometer (IR Gun) so that the temperature that it gives you will have a good correspondence with the internal temperature of the burger, or

  3. You need to cross-calibrate the temperature of your cooking surface temperature (using direct contact temperature measurement and time the cooking of each hamburger.

Each of these three methods can be cost-effective and practical for the measurement of proper cooking temperature--the last and strongest line of defense against E. coli pathogenic strains.

Let's call this the "poke it" | "shoot it" | "time it" collection of practical methods.

The "Poke-It" Practical Method

There is an effective, disposable temperature stick that will give an immediate indication of the internal temperature of a cooked hamburger. It is called the T-Stick.  The reactive, food safe sensor dot is in the tip.  Stick it in--if it turns color, you have passed the RULE.  Very simple.

Shown here (left side image) are some T-Sticks that have been set for 160 F.   They will give a reading after 5 seconds that is very representative of the internal temperature of a cooked hamburger.

T-Sticks are easy to use.  Three steps: insert, wait 5 seconds, remove.  If the square is black, the critical temperature is confirmed.

T-Sticks are proven and tested and can be used as part of a validated program in your organization. 

 

 

 

The "Shoot-It" Practical Method 

Research evidence has shown clearly that the outer skin temperature of a cooked hamburger will show a direct and predictable relationship with the internal, core temperature. Since the RULE is all about the core temperature of a hamburger, we seem to have something here. The system works like this:

  • Cook a hamburger on the actual equipment in the retail environment.
  • Carefully measure the internal temperature with an accurate digital thermometer or a T-Stick
  • Take a temperature reading of the outside of the hamburger with a good IR thermometer.
  • Find out the external temperature that corresponds to the RULE internal temperature - that will be your cooking criterion ("non-contact equivalent temperature" = NCET).
  • When cooking hamburgers, shoot each one and do not stop cooking until the NCET is reached.

The temperature of step 2 will always be lower than the temperature of step 3, but the importance is that there is a good correlation between these temperatures, so you can set a HACCP criterion for the IR temperature at a higher temperature, and thus be assured that you have a criterion that will allow you to conform to the RULE without having to cut burgers and actually poke the burgers to get a temperature.

Advantages of the "Shoot It" method:

  • Quicker
  • Less costly in the long run, since you have only the one-time investment in hardware.
  • Works with thin burgers (more difficult with the T-Sticks)

 

The "Time It" Practical Method

If the hamburgers that you cook are of uniform thickness, then it is a matter of physics that determines the heat accumulation rate at the core of the burger.  The longer the burger is cooked on a cooking surface of known temperature, the higher the core temperature of the burger gets.  It is a quite predictable relationship.  To set this up, you need to

  • Take a series of careful measurements of the actual cooking surface you will use (most guidelines recommend that you take seven measurements in corners and triangle in the middle)

  • Cook several hamburgers on the actual equipment in the retail environment for different times

  • Carefully measure the internal temperature with an accurate digital thermometer

  • Determine the cooking time that gets you into compliance with the RULE

  • Periodically recheck by repeating steps 1-4 above.

Some Considerations on Choice of a Practical Method

If you are considering some type of action to ensure the proper cooking of hamburgers in your operation, here are some comparative thoughts about the three methods:

Method Advantages Disadvantages Equipment and Supplies
"Poke It"
  • Quickest training period

  • Unequivocal result

  • Approved and tested

  • No need to run your own "calibration experiment"

  • Recurring cost

  • Doesn't work with thin hamburgers very well

  • Can take more time than other methods

  • If you run out of probes, you are out of compliance

T-Sticks
"Shoot It"
  • Probably the easiest to actually do day-in and out

  • Supported by scientific data

  • Accurate to about 3F, so you need a little slack in the cross-calibration

  • Need to run your own "calibration protocol"

  • Technique is very sensitive to burger thickness - if this changes, then calibration is not good

IR Thermometer with integral probe (we can recommend)


T-Sticks

"Time It"
  • Useful if there is an automated cooking procedure or cooking is in "batches"

  • Approved and tested

  • Doesn't require a measurement step

  • Accurate to about 3F, so you need a little slack in the cross-calibration

  • Need to run your own "calibration protocol" and test griddle temperature daily

  • Technique is very sensitive to burger thickness - if this changes, then calibration is not good

  • Not practical for "cook to order" operation - each individual burger would need their own timer

Thermocouple thermometer for taking reference internal temperatures (many choices...we recommend that you call us with information about your budget, personnel and frequency of use)

Griddle probe for the thermometer

Digital Cooking Timer (commercially available everywhere)

One program will be right for your operation.  Consider Global Sensors as your source for the materials and equipment that you will need--we offer discounts and excellent customer service. We can also help you to set up a cross-calibration program (the details are more than we can put here). 

Please call us on our the sales line or send us an email.


References

B. W. Berry and M. E. Bigner-George, 2001 "POSTCOOKING TEMPERATURE CHANGES IN BEEF PATTIES"  Journal of Food Protection: Vol. 64:9:1405 1411.

Juneja V. K., 0. P. Snyder, A.C. Wlliams, and R. S Marmer, 1997  "THERMAL DESTRUCTION OF ESCHERICHIA COLI IN HAMBURGER" Journal of Food Protection: 10:1163-1166.

M. E. Coleman and H. M. Marks, 1999 "QUALITATIVE AND QUANTITATIVE RISK ASSESSMENT" Food Control, Volume 10(4): 289-297

W.R. Windham, C.E. Davis and B.G. Lyon, 1998 "PREDICTION OF ENDPOINT TEMPERATURE BY VISIBLE AND NEAR-INFRARED REFLECTANCE SPECTROSCOPY IN HOME-STYLE COOKED GROUND BEEF PATTIES" TEKTRAN - United States Department of Agriculture, Agricultural Research Service 



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